Field of the Invention
The present invention relates to the hydroxylation of phenols or phenol ethers, and, more especially, to the hydroxylation of phenols or phenol ethers using hydrogen peroxide.
Description of the Prior Art
The preparation of diphenols by hydroxylation of phenol or substituted phenols, using hydrogen peroxide, is known to this art.
French Patent No. 69/45,467, published under No. 2,071,464, describes a process in which the reaction is catalyzed by a strong acid such as, for example, perchloric acid or sulfuric acid.
German Patent No. 2,410,742 describes a process similar to the above, in which hydrogen peroxide is employed in the form of a virtually anhydrous organic solution.
These two processes are of considerable interest and the former is utilized industrially.
However, for a number of years attempts have been made to catalyze the hydroxylation reaction using solids which are not dissolved in the medium, in order to simplify their separation from the reaction medium and their recycling if desired, and to avoid the saline by-products which are formed in most cases when the dissolved acidic catalysts are removed.
Thus, French Patent 81/17,023 (published under No. 2,489,816) recommends the use of titanium silicalite as a heterogeneous catalyst for the hydroxylation of aromatic compounds using hydrogen peroxide.
The fine size of the catalyst particles which are employed makes such particulates very difficult to separate from the reaction medium and their recycling questionable, whereas, in an industrial process, it is essential to be able to recycle a costly catalyst.
In order to overcome this problem of catalyst separation, it has been proposed, in published European Patent Application No. 200,260, to employ agglomerates of these fine particles of titanium silicalite.
Nonetheless, a need continues to exist in this art for a heterogeneous catalysis of the hydroxylation reaction of phenols or phenol ethers using hydrogen peroxide, which can be employed industrially under economically acceptable conditions.
Cf. U.S. Pat. No. 3,580,956, FR-A-2,563,446 and GB-A-2,116,974.